The field of the invention relates to lasers and certain related methods, and in particular to micro-cavity lasers and related methods.
In the now rapidly expanding technology relating to the use of optical waveguides and in particular fiber optic waveguides, a number of discrete devices and subsystems have been developed to modulate, route or otherwise control, optical beams that are at specific wavelengths. Present day communication systems increasingly use individual waveguides to carry densely wavelength multiplexed optical beams. Thus, there is a need for a self-contained device and related methods which can induce a lased output in a frequency range of interest. Currently, the telecommunications industry uses frequencies in the 1550 nm range.
It is known to one of ordinary skill in the art how to couple a waveguide to an optical resonator so as to transfer optical power to the resonator from the waveguide or from the waveguide to the resonator. It is also known to one of ordinary skill in the art that power circulates in a resonator preferentially at resonant frequencies corresponding to optical modes of the resonator. For the purposes of discussion the terms resonance and optical mode will be used interchangeably herein. Likewise the principles associated with lasing action in resonators and in particular rare earth doped resonators and micro-resonators are well understood to one of ordinary skill in the art. The terms micro-cavity, resonator, micro-resonator will be used interchangeably herein. Discussion of these concepts can be found in one or more of the following references, the disclosure of each of which is incorporated by reference herein as if set forth in full hereat: V. Lefevre-Seguin and S. Haroche, Mater. Sci. Eng. B48, 53 (1997); J. C. Knight, G. Cheung, F. Jacques, and T. A. Birks, Opt. Lett. 22, 1129 (1997); M. Cai, O. Painter, and K. Vahala, Phys. Rev. Lett. 85,74 (2000); M. Cai and K. Vahala, Opt. Lett. 25, 260 (2000); V. Sandoghdar, F. Treussart, J. Hare, V. Lefevre-Seguin, J. M. Raimond, and S. Haroche, Phys. Rev. A 54, 1777 (1996); W. von Klitzing, E. Jahier, R. Long, F. Lissillour, V. Lefevre-Serguin, J. Hare, J. M. Raimond, and S. Haroche, Electron. Lett. 35, 1745 (1999); P. Laporta, S. Taccheo, S. Longhi, O. Svelto, and C. Svelto, Opt. Mater. 11,269 (1999); V. B. Braginsky, M. L. Gorodetsky, and V. S. Ilchenko, Phys. Lett. A 137,393 (1989); A. Serpenguzel, S. Arnold, and G. Griffel, Opt. Lett.20, 654 (1995); V. S. Ilchenko, X. S. Yao, and L. Maleki, Opt. Lett. 24,723 (1999); M. L. Gorodetsky and V. S. Ilchenko, J. Opt. Soc. Am.B 16, 147 (1999); T. Baer, Opt. Lett. 12, 392 (1987); G. H. B. Thompson, Physics of Semiconductor Laser Devices (Wiley, New York, 1980); T. Mukaiyama, K. Takeda, H. Miyazaki, Y. Jimba, and M. Kuwata-Gonokami, Phys. Rev. Lett. 82, 4623 (1999);
The theoretical concept of inducing lasing action in a micro-resonator doped with Nd is discussed by F. Treussart, et al., in Eur. Phys. J. D 1, 235 (1998), the disclosure of which is incorporated by reference herein as if set forth in full hereat. This reference, however, presents a device which relies on the use of prisms to couple to the laser resonator. Such a configuration presents many difficulties and limitations on its use in the field, as it requires delicate and precise alignment, is bulky and not easily adaptable common use and does not produce an output frequency which is currently of most use in the telecommuting industry. Additional limitations of these and other devices include low emission and coupling efficiencies.
The present invention overcomes these and the other limitations of the prior art by providing a compact, self-containable laser source that is directly coupled to an optical fiber waveguide. Optical fibers, in addition to being very important in modem optical communications systems, provide a very convenient means to convey both optical pump power to the laser as well to convey emitted laser radiation from the laser resonator. The ability to directly couple laser emission to an optical fiber is therefore of great practical significance. The output frequency of the present invention can be tuned both by design (based on choice of certain materials and/or dopants utilized) and dynamically (by varying the frequency of the laser pump signal) and by incorporation of grating structures into the micro-cavity. The present invention also provides a laser source with improved emissions and increased coupling efficiency between the waveguide and the resonator. Finally, the each of the preferred embodiments can be made to be robust and easy to implement in a variety of configurations and uses.
The present invention is directed to a micro-cavity laser and certain related methods. The devices and methods of the present invention are useful for creating laser signals having a frequency within a desired range by optically coupling an optical pump signal in a waveguide to a micro-cavity optical resonator, which resonator includes an active medium which is capable of providing optical gain upon pump excitation and which resonator and pumped active medium result in lasing action at a frequency within the desired output range. In the preferred embodiments, the waveguide is a fiber waveguide of any configuration and the coupling between the fiber waveguide and the resonator is by means of an optical couple between a fiber taper in the fiber waveguide and the micro-cavity optical resonator. In the preferred embodiment the fiber waveguide serves to both transport optical pump power to the resonator to excite the amplifying medium as well as to collect lasing emission from the laser cavity and transport it to elsewhere. The fiber waveguide and the resonator are preferably critically coupled at the pump wavelength so as to maximize pump power coupling to the active medium. In addition, it is possible and important to phase match the fiber taper and the micro-cavity resonator so as to maximize the coupling efficiency between these two elements of the present invention.
In another embodiment two fiber waveguides are coupled to the micro-cavity and each is optimized for coupling of pump power or collection of laser emission. In this embodiment phase matching could be employed to perform this optimization.
The micro-cavity optical resonator can have a variety of shapes including, without limitation, a microsphere, one or more micro-rings, racetracks or disks incorporated on a substrate or one or more micro-rings or disks formed on the fiber waveguide itself. Indeed, it is preferable in certain applications for there to be more than one micro-cavity resonator on a single fiber waveguide, for example in creating a multi-wavelength laser array along the fiber waveguide.
The output of the micro-cavity laser of the present invention can be tuned by varying the pump wavelength and/or utilizing different material composition for the micro-cavity optical resonator. In addition, internal structures such as optical gratings can be added to the optical path within the resonator so as preferentially select a particular optical mode for lasing and in turn the frequency. The laser can also be made to operate continuous wave or self-pulsing.
Accordingly, it is an object of the present invention to provide a micro-cavity laser having the advantages detailed herein.
This and other objects of the invention will become apparent to those skilled in the art from a review of the materials contained herein.